Typical control valves including disc variable valves used for the purposes of controlling the flow rate hardly control the flow rate precisely since the location of the opening/closing part of the valves and the open area of the flow path are not linearly related. Also, the shape of the flow path inside the valve drastically changes to fluctuate the velocity and pressure of fluid to thereby cause a turbulent flow, resulting in great pressure loss, flow noise and vibration. If the fluid is liquid, a very low pressure is partially formed inside the fluid and the separated gas of the liquid generates cavitations. To control the typical valves as above, an additional motor is required to rotate the rotation part of the valves and the control system becomes complicated.
As to one usage of the variable valve, a disc variable valve which is used for an automotive exhaust system is attached to a first end of an exhaust pipe as shown in (a) in FIG. 1. Automotive muffler is used to reduce exhaust noise by gradually decreasing the pressure of exhaust gas since high temperature and high pressure pulsating exhaust gas causes great noise due to a drastic change in pressure if being emitted to the atmosphere as is. If the pressure of the exhaust gas emitted from the muffler (“back pressure”) increases, the exhaust noise is reduced, but exhaust resistance increases and the engine power drops. By contrast, if the exhaust resistance is reduced to prevent the power loss of the engine, the exhaust noise aggravates. Accordingly, if the variable valve is attached to the exhaust gas discharger, back pressure increases in a low speed area where the exhaust noise is important, and decreases in the medium and high speed area where the engine power is important, to thereby solve the foregoing problem which arises in the design of the muffler.
As shown in (b) in FIG. 1, a valve plate of a conventional disc variable valve which is used for an automotive muffler is initially closed by a spring and open when back pressure rises to exceed the force of the spring with the flow rate increase. It is important to understand the correlation between the back pressure according to the flow rate and a spring constant to apply the variable valve to the muffler. However, in the case of a conventional disc variable valve, an opening area does not linearly increase according to an opening angle of the disc and it is very difficult to calculate the flow rate which is discharged through the opening area. Accordingly, a lot of tests should be conducted for diameters of exhaust pipes in which valves are attached with respect to various engines to identify the correlation between the back pressure and the spring constant, and each test formula should be found. Thus, it is not easy to manufacture an appropriate variable valve, and the common application of manufactured variable valves to other mufflers is limited.
In the case of the disc variable valve, opening the valve makes the flow path very complicated, and the flow of the fluid drastically changes, and causes noise and vibration due to a turbulent flow. To that respect, the variable valve may reduce the pulsating noise from the engine, but the flow noise from the variable valve increases, and the overall improvement for the exhaust noise is not that great or may become worse.
Conventional flowmeters which measure the flow rate through a differential pressure by using a ventury tube or nozzle has its cross sectional area fixed to measure the differential pressure, and are not appropriate for measuring a wide range of flow rates. If a wide range of flow rates should be measured, at least two flowmeters which have different ranges should be used simultaneously or sequentially measure the flow rate to overlap a part of the measurement range. In the former case, the flowmeters cannot be used adjacently in a desired location due to an interference of the flow. In the latter case, the adjustment of the overlapping range after the measurement is required and the flowmeters should be replaced.
To solve the problem of the typical control valve, the applicant filed application for “aperture-shaped active control variable valve” with Korean Patent Application No. 10-2007-0048965. This invention arranges a plurality of aperture plates in a ring shape on an aperture frame to have a semi-spherical or cone shape so that the valve is attached to the inside or end of the pipe in which fluid flows. The valve includes a means to apply a consistent force to an aperture surface including a plurality of aperture plates to control the exit diameter of the aperture and control the flow rate or pressure.
The present invention is an improved invention of Korean Patent Application No. 10-2007-0048965.